In general, a ballpoint pen employing an oil-based ink conventionally has a simple structure installing in its holder a ballpoint-pen refill having a ball-holding metal tip engaged with one end of the ink reservoir tube.
While an oil-based ballpoint pen having a structure described above can be provided at a low price, it should be constructed in such a manner that the gap between the ball and the tip should be reduced in order to avoid the drip of the ink via the gap of the ball and the tip when the tip is in a downward direction, i.e., when the pen stands on its head, and it also should have an ink whose viscosity at ambient temperature which is as high as thousands to ten thousands mPa·s. Accordingly, it has a heavy touch upon drawing, and tends to exhibits a pale line. Also in order to avoid the blurred line due to the evaporation of an organic solvent from the pen tip, the organic solvent should be one that has a high boiling point and is difficult to be evaporated.
While a conventional ink for a ballpoint pen is intended to be used in writing on the surface of a paper and has no practical problems with regard to the dryness of a drawn line because of the permeation of the organic solvent in the ink into the internal region of the paper, it poses a problem such as a deposition of a still-wet ink onto a hand or a dirt on a non-written blank on the paper upon touching the drawn line with a hand due to no permeation of the organic solvent when it is drawn on a non-permeable material.
Also while it was attempted to reduce the viscosity of an ink for the purpose of obtaining a light pen touch and an intensely colored line, no sufficient performance was obtained in the drawing on a non-permeable material described above (JP-A-63-309571).